“We support the merger of American and US Airways because it is based on growth which benefits consumers and our communities,” the mayors wrote. “A hub airport is only as good as the route network it supports, and our cities represent hubs throughout the United States that would benefit from a broader route network.”

The letter was signed by Democratic and Republican mayors, and the support of Emanuel — a former chief of staff to President Obama — could give the plea added weight with the administration.

American and US Airways announced their proposed $11 billion merger in February,
but the DOJ filed a lawsuit to block the combination this summer.

US Air and American Airlines have responded to the DOJ lawsuit by arguing that they have less overlapping non-stop flights, though the Justice Department counters that the companies should also count flights with layovers.

The hub city mayors sided with the airlines.

“The combination of American Airlines and US Airways creates a better network than either carrier could build on its own,” the mayors wrote, adding that the incresae in passenger traffic "will multiply the beneficial effects those airports have on jobs and our local economies.”

The mayors argued US Air and American would not be able to compete with other airlines that have merged in recent years, like Delta and Northwest and United and Continental airlines, if their merger is not approved.

That could put their airports at a disadvantage against cities that are home to other airline hubs, the mayors said.

“Without this merger, American and US Airways will be at a permanent competitive disadvantage to Delta and United, each of which has been allowed to build superior route networks through mergers that were cleared by the Justice Department, the latter under your watch,” the mayors wrote. “

"The long-term prospects of American and US Airways will be imperiled. But even worse than the impact on the merging companies, failure to clear the combination of American Airlines and US Airways will put our cities at an unnecessary competitive disadvantage to Atlanta, Newark and other hubs that directly benefit from the Delta and United mergers.”